School of
Information Technology and Electrical Engineering

Speaker: Mr Lakshitha Naranpanawe
Seminar Date: Fri, 05/01/2018 - 14:00
Venue: 78-622
Host: Prof Tapan Saha

Seminar Type:  PhD Thesis Review

Abstract: 

Power transformer is one of the critical equipment for the reliable operation of electric power grid. An unexpected failure of a power transformer can cause a significant impact on the stability of power system. Therefore such failure has the potentially to initiate required conditions for a system blackout. On the other hand, power transformer is one of the most expensive single unit in a power network. Therefore utilities are reluctant to replace the old transformers exclusively based on the operating life. The replacement of such unit is typically based on the total life cycle cost, which includes various expenses associated with operation, maintenance, replacement and system reliability. However such cost estimation is impossible without knowing the current operating condition of the unit including mechanical integrity of the winding structure.

Maintaining mechanical integrity of the transformer winding is vital to withstand the transformers against short circuit faults that exert strong electromagnetic forces on the winding. Due to grid expansion both short circuit (SC) current magnitude and the frequency of fault occurrences are increasing making the SC withstand capability a major concern, especially for transformers operating beyond the designed life. Transformer winding is clamped at the top and bottom ends to obtain the required withstand capability against mechanical impacts. Further, with ageing progressive loss of winding clamping pressure occurs reducing the short circuit withstand capability of power transformers. However, condition monitoring of winding clamping system is rarely discussed and information on the changes in power transformer winding clamping pressure under different operating conditions is scarce.

This research investigated methodologies to improve the condition monitoring of transformer clamping pressure on operating transformers. As clamping pressure is highly dependent on the condition of pressboard a set of comprehensive laboratory investigations of the out-of-plane compression behaviour of pressboard was conducted. The experimental results combined with an FEM based material model were used to quantify the effect of moisture, temperature and ageing on pressboard compression behaviour. The finite element modelling was further used to investigate the effect of pressboard condition and winding faults on the clamping pressure. Parallel to above investigations, attempts were taken to use online transformer tank vibration signals to identify the changes in winding clamping pressure. This study proposes a methodology based on cepstral analysis to extract the vibration characteristics of the transformer winding and core form tank vibration signals.

Biography: 

Lakshitha Naranpanawe received his B.Sc. in Electrical and Electronics Engineering from The University of Peradeniya, Sri Lanka in 2012. He served as an Electrical Engineer (Operations) at Ceylon Electricity Board for one year. Currently, he is a final-year PhD Student in the Power & Energy Systems Group at the School of Information Technology and Electrical Engineering, The University of Queensland, Australia. His research interests include condition-monitoring of power transformers and use of online vibro-acoustic methods for transformer clamping pressure monitoring.